User's Manual

APPENDIX C

Calculating Transmit Power

The following information explains how to calculate the input and output power to and from the Converter:

1. Using Appendix A, Table A, convert the output power of the radio device from milliWatts to dBm.

The Model CA2458 Converter ODU is optimized to work with input powers between +3 dBm and

+8 dBm.

2. Calculate the cable attenuation at 2.4 GHz as follows:

Determine the attenuation for the length of your cable at 2.4 GHz. Use the cable manufacturer’s

specifications or, for convenience, refer to Table B for typical values. For example, Table B

shows that typical attenuation for LMR-400 is about 7 dB per 100 foot at 2.4 GHz. Add 2 dB of

misc. loss for connector, adapter cable and DC injector. Subtract total attenuation from the

radio’s transmit power.

3. Calculate the maximum power that can be expected at the Converter when mounted on the pole

as follows:

WLAN card output (dBm) - Cable loss (dB) - Misc. Loss =

Signal level @ CA2458 input (dBm)

For example, a radio with +15 dBm output and 75 feet of LMR400 (about 5 dB of loss) would

have the following input level to the converter/amplifier:

+15 dBm – 5 dB – 2 dB = +8 dBm

If the input to the Converter exceeds +10 dBm by your calculations, an attenuator pad or a

longer/higher loss coax cable will be necessary between the WLAN card and the DC injector.

Alternatively, a special version of the Converter may be obtained from YDI that will accept higher

transmit input power.

NOTE: Do not attempt to over drive the Converter. Doing so does not only puts the converter

into hard compression and does not increase output power. It only raises the sidebands,

which pollutes adjacent channels and may result in harmful emissions outside the 5.8

GHz Spread Spectrum band.

Transmit power at 5.8 GHz would then be:

+8 dBm +14 dBm = +22 dBm

NOTE: Never put attenuator pads in the cable between the DC injector and the

Converter/Amplifier since there is a +15VDC voltage on the cable. Doing this would

prevent DC power from reaching the amp and will damage the attenuator. A longer

cable or one with higher signal loss could be used.

Calculating Effective Isotropic Radiated Power (EIRP)

EIRP is defined as the sum of the power feeding an antenna plus the gain (in dBi) of that

antenna. For example, +22 dBm of power into a two foot dish or flat panel antenna with 27 dBi

gain would be the following dBm EIRP:

+22 dBm + 27 dB = 49 dBm (80 watts) EIRP